Electric trains are powered through overhead copper conductor lines, the power being conveyed via a pantograph attached to the roof of the train. The conductor lines are usually powered by 25 kV AC supplied from power stations along the route of the lines. As the power stations are not synchronised, a peak-to-peak difference of up to 50 kV AC can occur where two power supplies meet along the length of a conductor line. It is important to ensure that the pantograph does not register the difference in power supplies as otherwise a large electrical load would be placed on it, which could damage it and other electrical equipment in the train. As it is impractical to synchronise the power stations, they are normally isolated from each other by the provision of an assembly known as a neutral section insulator on each conductor line.
It is desirable that the pantograph does not detect the presence of the neutral section insulator on the conductor lines as, apart from electrical loading, it would then also be subject to variable reaction forces, which would be conveyed to the train to cause “humping”.
The neutral section insulators that are currently on the market include those provided by Siemens GmbH, Arthur Flury AG and Furrer & Frey AG. The neutral section insulator of Siemens GmbH, consisting of two insulator body rods mounted on plates with copper conductors being clamped thereto, is mechanically quite different from the conductors and increases the scope of shock loading on the pantograph. Although the height of the neutral section insulator can be adjusted relative to the copper conductors in order to align them as closely as possible in the vertical plane, the catenary member that is used for such adjustment makes the neutral section insulator assembly more bulky, increases its structural and mechanical difference from the conductor lines, and complicates its installation. An arcing horn is provided in this neutral section insulator to channel the power dissipation that occurs if the pantograph registers the difference in power supplies. However, it is not particularly effective in this role, as often sparks are seen to form where the pantograph attaches to the neutral section insulator. Furthermore, this neutral section insulator is expensive, wears quickly (it needs to be replaced roughly every eight months), and requires monthly maintenance to turn the insulator body sections (which wear out by virtue of point contact with the pantograph).
Accordingly, it is desirable to provide a neutral section insulator that effectively isolates the conductor lines without posing a “gap” to a pantograph traversing the length of the lines, is maintenance-free during the lifetime of the product, cheap to produce and simple to install.
According to an embodiment of the present invention, there is provided a neutral section insulator for use with an overhead railway conductor line, which neutral section insulator is disposed between the ends of the conductor line when in use and comprises an insulator body to isolate the ends of the conductor line from each other; wherein the neutral axis of the neutral section insulator is such that when the neutral section insulator is in use the neutral axis is aligned closely with the neutral axis of the conductors on its either side and the height of the insulator body is chosen so that the stiffness and the dynamic mass of the neutral section insulator closely match those of the conductors on its either side in both the vertical and horizontal planes.
The structural and mechanical profile of a neutral section insulator embodying the present invention is constructed to closely correspond with that of railway overhead copper conductor lines in order to minimise the scope of being registered by a pantograph, this being achieved by closely aligning the neutral axes (median bending line) of the neutral section insulator and the conductors on its either side, and by closely matching the stiffness and the dynamic mass of the neutral section insulator and the conductors in both the vertical and horizontal planes.
An embodiment of the present invention provides a continuous running surface to the pantograph that is both coplanar with the conductors on its either side (so that the pantograph is not subject to shock loading) and narrow (since misalignment with the pantograph would cause a severe twisting action in the neutral section insulator), and also provides the advantage that the drag imposed by the neutral section insulator on the pantograph is equal to, or less than, that exerted on it by the conductors.
Furthermore, an embodiment of the present invention provides isolation over a distance in excess of 1.5 m, even when the pantograph (which is 0.2 m in width) attaches to the neutral section insulator and effectively increases its length to about 1.7 m.
An embodiment of the present invention is capable of withstanding the 15 kN loads, which are hung every few hundred meters along the length of the conductor lines in order to provide tension, without degrading.
An embodiment of the present invention provides all the above-discussed advantages in adverse environmental conditions such as rain, snow, contamination, etc.